Flame combustion synthesis

A process called flame combustion synthesis is widely used to manufacture catalysts containing carbon black, fumed silica, or titania [277-279]. 

Jensen, J. R. Johannessen, T. Wedel, S. livbjCTg, H. A study of Cu/Zn0/Al203 methanol catalysts prepared by flame combustion synthesis. Journal of Catalysis 2003, 218,67-77. 

An important topic of research is the introduction of the catalyst in the microreactor. In brief solid catalysts can be incorporated on the interior of micromachined reaction channels, prior to or after closure of the channel, by a variety of strategies anodic oxidation, plasma-chemical oxidation, flame combustion synthesis, sol-gel techniques, impregnation, wash coating, (electro-)plating, aerosols, brushing, chemical vapor deposition, physical vapor deposition and nanoparticle deposition or self-assembly. Some of these methods can be applied in combination with photolithography or shadow masking. 

CNTs can also be produced by diffusion flame synthesis, electrolysis, use of solar energy, heat treatment of a polymer, and low temperature solid pyrolysis. In flame synthesis, combustion of a portion of the hydrocarbon gas provides the elevated temperature required, with the remaining fuel conveniently serving as the required hydrocarbon reagent. Hence, the flame constitutes an efficient source of both energy and hydrocarbon raw material. Combustion synthesis has been shown to be scalable for a high volume commercial production. 

Modem computational programs [4] and thermodynamic tables [5] now make it possible to explicitly calculate metal-oxygen flame temperatures, thereby opening up a unique aspect of combustion thermodynamics that could be important in the consideration of metal as fuels and as reactants in combustion synthesis. 

Saita et al. [215] used hydriding combustion synthesis for a direct production of TiFe. In the experiments, an exothermic reaction of Ti with hydrogen (Ti -i- i = TiHj + 144 kJ) was utilized for HCS of TiFe because the adiabatic flame temperature of this reaction was estimated to be 2,000°C, which is sufficiently high for melting both iron and titanium. A 1 1 molar mixture of elemental Ti and Fe pow-... 

McKinnon JT, Bell WL, Barkley RM (1992) Combustion synthesis of fullerenes. Combust Flame 88 102-112... 

M. Murayama and K. Uchida. Synthesis of Uniform Diamond Films by Flat Flame Combustion of Acetylene/Hydrogen/Oxygen Mixtures. Combust. Flame, 91 239-245,1992. 

If we restrict ourselves to laminar flames, it appears possible to understand quantitatively how the concentration of all species present is distributed throughout the flame zone and how this distribution varies with temperature and additives. This possibility makes it attractive to consider ways in which intermediates may be withdrawn from the flame zone or to attempt to produce species which do not reach equilibrium within the flame zone. It is, of course, still practical to produce useful substances by combustion to a favorable equilibrium, but this type of synthesis does not require much knowledge of the flame zone. It is useful however to use a flame in synthesis in this way in order to prevent contact with surfaces or to regulate the coagulation of solid products. 

Pratsinis, S.E., Flame aerosol synthesis of ceramic powders, Prog. Energy Combust. ScL, 24, 197, 1998. 

An interesting approach in making mullite powders has been via combustion synthesis [36], An aqueous heterogeneous redox mixture containing aluminum nitrate, silica fume (soot), and urea in the appropriate mole ratio is mixed together. When rapidly heated to 500°C, the mixture boils, foams, and can be ignited with a flame. The process yields weakly crystalline mullite powder in less than 5 min. Fully crystalline mullite can be obtained by incorporating an extra amount of oxidizer, such as ammonium perchlorate in the solution. 

Figure 2. Schematic diagram of various CVD techniques for diamond synthesis, (a) HFCVD (b) MW PACVD (c) ECR MW PACVD (d) DC PACVD (e) RF PACVD (0 DC thermal plasma CVD (g) RF thermal plasma CVD (h) flame (combustion) CVD.l (Reproduced with permission.)...

Combustion synthesis of diamond films fi om atmospheric pressure oxyacetylene flame was first reported by Hirose in 1988.This technique, as shown schematically in Fig. 2h, has been demonstrated to be a potentially very important means of growing diamond (Table 1). In Hirose s experiments, linear growth rates of100-200 pmh were achieved. The results were then confirmed by Hanssen et al.l l In Hirose s experiments and most of those that followed, the oxyacetylene torch was typically run with... 

T. Tani, N. Watanabe, K. Takatori Emulsion combustion and flame spray synthesis of zinc oxide/silica particles, Journal of Nanoparticle Research 5(1-2), 39 6 (2003). 

Yeh CL, Zhao E, Ma HK (2001) An experimental investigation of combustion synthesis of silicon dioxide (Si02) particles in premixed flames. Combust Sci Technol 173 25-46... 

Gas phase combustion synthesis offers the potential to produce bulk quantities of particles with controllable morphologies and chemistries. In this paper we demonstrate the use of an atmospheric pressure flame to produce a nanocomposite with unique magnetic properties and investigate the salient features of their formation through the application of in-situ diagnostics and modeling. 

Flame spray pyrolysis and ultrasonic spray combustion represent other methods leading to perovskites with comparable morphologies with those produced by solid-sohd reactions and solution combustion synthesis [23]. 

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